Do you mean "Why is it take but not takes"?
The third person plural form is take: they take the same course.
take, took, taken, taking, takes
- I take the book. We take the book. They take the book. You take the book. Let her take the book. Why should I take the book?
- I took the book. He took the book. She took it with her. We took it back. They took it somewhere. Who took the book?
- The book has been taken. It was taken somewhere. You have taken it, haven't you?
- I am taking it with me. Why are you taking it? What are you taking with you? We are taking her with us. They are taking him with them.
- He takes it with him every day. It takes a village to raise a child. It takes two to tango. That takes the cake!